How should I charge to bring my coffee truck to a wedding

[TOEspresso]

I have been asked to bring my coffee truck to a wedding and I'm trying to figure out how to charge for this. The wedding will have 250 attendees and the bride is proposing I be "open" from 5:30 - 9:30. I'm thinking that I should charge her a "rental" fee up front and then a fixed price for each drink I provide. Does anyone do this differently? Does this sound like a reasonable approach. Any guidance you can provide will be helpful.

 

[Buskers Brew Coffee]

I would suggest a buy out, based on the number of guests and factor how many drinks they may want.

That maybe factors to 1/2 - 3/4 will want 1 drink average and then offer a buy out on tiers, like a bar.
1-2 hours of open coffee drinks and then guest pay after that or a full buy out for the evening at $$$ amount.

Have a minimum $ that you need to make/charge in case drink ordering is lower than anticipated or due to weather or other factors.